Approximately 68-80% of youth will experience at least one potentially traumatic event during their childhood with about one third experiencing more than one traumatic event. Exposure to traumatic events markedly elevates the risk of developing posttraumatic stress disorder (PTSD) and associated impairment. Despite advances in effective trauma-focused treatments for children, the lack of efficient, accessible, personalized, and cost-effective trauma treatment for children is a major public health concern. Thus, there is a critical need for interventions to improve efficiency, access, and cost-effectiveness and to offer tailored approaches that meet the unique needs of the child. The present study builds on our NIH-funded pilot work (1R34MH092373- 01A1) that developed an innovative Stepped Care Trauma-Focused Cognitive Behavioral Therapy (SC-TF- CBT). The purpose of the proposed study is to examine how to optimize the efficiency (e.g., via matching children to appropriate treatment dosage at baseline, utilizing second-stage tailoring variables, and identifying mechanisms of change) and cost-effectiveness of Stepped Care TF-CBT. The long-term goal is to develop an effective, efficient, accessible, and cost-effective adaptive Stepped Care TF-CBT intervention that can be available to more trauma-exposed children, and to advance knowledge about service delivery approaches that may be applicable to providing treatment for other childhood mental health disorders. Our goal is consistent with the strategic objective to Develop New and Better Interventions that Incorporate the Diverse Needs and Circumstances of People with Mental Illness, and the research priorities that call for trials that foster prescriptive, personalized mental health care, incorporate tailoring variables to match patient interventions, improve access to services, decrease costs of services, and incorporate measures of putative mechanisms of action in trials in real world settings. In a randomized clinical trial with 216 children ages 4 to 12 years at community-based agencies, we are proposing the following aims: Aim 1: To examine Stepped Care TF-CBT (e.g., starting with Step One parent-led, therapist-assisted treatment and then either maintenance or Step Two TF-CBT) relative to standard TF-CBT (e.g., therapist-led treatment); Aim 2: To examine tailoring variables that could be used to individualize (i.e., tailor) the decision of which children should be assigne at baseline to Stepped Care TF-CBT versus standard TF-CBT; Aim 3: To examine if changes in the potential mechanisms of change variables (e.g., fear arousal, maladaptive cognitions, negative expectancy, and fear toleration) mediate treatment on child PTSD symptoms (PTSS) and impairment; and Aim 4: To examine the economic cost of delivering Stepped Care TF-CBT versus standard TF-CBT. Children with PTSD are at considerable risk for numerous biopsychosocial problems. Without accessible, effective treatment, these problems tend to persist into adulthood. This study will yield clinically important data which will improve the valu and efficiency of treatment of children with PTSD, thereby reducing childhood PTSD and related societal impacts and costs.